This application is related to combustion sensors, methods of using variable resistance oxygen sensors as combustion sensors, and related devices and systems for use with periodic combustion processes, such as in internal combustion engines.
In internal combustion engines under certain conditions, combustion may not take place properly. For example, a combustion misfire event occurs when the air and fuel mixture does not combust in a cylinder during a given cycle. Combustion misfire events result in loss of power, poor emissions, performance, and the potential for combustion to take place in the exhaust stream, resulting in damage to the exhaust management components. Often such phenomena take place intermittently, yet may still have a significant impact on the engine and/or emission system performance.
Accordingly, it is desirable to detect when combustion misfire events occur in order for corrective measures to be implemented. Currently, pressure sensors located in the compression chamber are used to detect misfire events. However, such pressure sensors are expensive due to the need to design them for the harsh environment of the combustion chambers. Combustion misfire events may also be detected by monitoring the angular velocity of the engine's crankshaft for minor variations in the expected rotation of the crankshaft as the result of misfiring; however, this approach requires complex algorithms to deal with the high signal to noise ratio inherent in this approach. Combustion misfire events may also be detected by monitoring analysis of the ionization current in the sparkplug circuit and/or optical measurement of the combustion process, both of which are better suited to basic research than commercial products.
As such, there remains a need for alternative combustion sensors for combustion engines, advantageously one that can be placed outside of the combustion chamber, such as in the exhaust plenum.